Current control device



Feb. 9,

CONTROL CURRENT ICONTROL m) 1965 p. w. KERMODE 3,169,194

CURRENT con'moz. DEVICE FIG; 1.

i 5 i 3 1% r LOAD CURRENT 0A.D 9m) I I v FIG. .2."-

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5| DAVID w. KERMODE 49 5 f ATTORNEYS.

2 Sheets-Sheet 1 Feb. 9, 1965 p. w. KERMODE 3,169,194

CURRENT CONTROL pEvIcs Filed May 19, 19.60 I '2 Sheets-Sheet 2 mmvroxDAVID w; KERMODE BY f K.

ATTOR NEYS.

United States Patent O 3,169,194 CURRENT C(ENTROL DEVICE, David W.Kermode, 107 Arondo, Ridgecrest, Calif.

Filed May 19, 1960, Ser. No. 30,389

4 Claims. (Cl. 367-18) (Granted under Title 35, US. Code (1952), sec.266) This invention herein described may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention relates to a current control device and inparticular to. a current control device utilizing a single transistorfor control of currents of from several to less than one microamperen IMechanical and electrical relays having moveable electrical contactpoints have been used for control of small currents. However, relays ofthis type are expensive and bulky and their repetition reliability, whenused for control of small currents,-is relatively lowbecause of thedifiiculty in applying constant pressure to the contact points.Transistors have also been used for the control of small currents.However, transistor circuitry has been confined to applications wherethe current to be controlled WaS either an integral part of the controlcurrent or the control current was balanced out by utilizingsymmetricalelectrical circuitry. Current dividing control devices for currents ofthe order of several microamperes have been complex or cumbersome unitcompared to the currents to be controlled. Such types'of control unitshave consisted of cascaded potentiometers, cascaded rheo stats andamplifiers. i i

. The present invention overcomes the aforementioned difliculties andprovide a current control method that is ettective forcurrents of fromseveral to less than one microampere. This is accomplished by reversebiasing the emitter, collector and base of a transistor and'by employingt-wo diodes. The load circuit isseries connected with the: emitter andcollector of the transistor and one diodev and the control circuit isseries connected with the emitter-and base of the transistor and anotherdiode. The diodes function to limit the operating range of the cireditby .preventingreverse current flow in the load and control circuits.

An object of the present invention is to provide a current controldevice which is simple, lightweight and of inexpensive construction;

Another object is to provide a current control device wherein loadcurrents of the order of from several to less than one micr-oampere areaccurately controlled in response to a control signal.

Still another object is to provide a limited current control deviceutilizing a single reverse biased transistor wherein the load circuitincludes the emitter and collector of the transistor and the controlcircuit includes the emitter and base of the transistor. i

A still further object is to provide a limited current control deviceutilizing a transistor wherein the use of diodes prevents reversecurrent from flowing in the load and control circuits.

Other objects and many of the attendantadvantages of this invention willbecome readily appreciated as the same becomes better understood byreference to'the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a schematic diagram of the preferred embodiment of the presentinvention;

:FIGJZ is a curve showing the relationship between control current andload current for the FIG. 1 device;

FIG. 3 is a schematic diagram of a further embodiment of the-presentinvention; j r i 3,169,194 Patented Feb. 9, 1965 FIG. 4 is a schematicdiagram of a still further embodiment of the present invention; and

FIG. 5 is a schematic diagram of a still further embodiment of thepresent invention.

The current control circuit shown in FIG. 1 includes a transistor 11having an emitter electrode "13, a collector electrode .15 and, a baseelectrode 17. The control circuit is a series circuit includingpotential source 19, rheostat 21, switch '23, diode 25, emitter 13 andbase 17. Potential source 19 is poled inthe control circuit with itspositive terminal directly coupled to base electrode 17, and itsnegative terminal coupled to emitterelectrode 13 through the othercircuit elements, which is opposite to the polarity relationships of apotential source for biasing the base circuit of a transistor initsnormal amplifieroperation, and Whichtends to generate current flowthrough the transistor between its emitter and base in a directionopposite to the direction of input signal current flow therebetween inits normal amplifier operation. The load circuit is a series circuitincluding potential source 29, load '31, emitter 13, collector 15 anddiode 33. Diodes 25 and 33 are forward biased by means of potentialsources 19 and 29, respectively. Potential source 2 9 i poled in theload circuit with its positive terminal coupled to collector 15 throughdiode 33, and its negative terminal to emitter 13 through load 31, whichis the'same as the polarity relationship of a potential source forbiasing the collector circuit in its normal amplilier operation, andwhich tends to generate current flow through the transistor between itscollector and emitter in a direction opposite to output signal currentflow therebetween in it operation as a conventional amplifier. The base-17 of transistor 11 is reverse biased by potential source 19 andemitter 13 and collector #15 are reverse biased by means of potentialsource 29. Diodes 25 and 33 are of the type having very high backvoltage resistance and very low back leakage current. The use of diodeshaving low back resistance and high back leakage current'will notnecessarily prevent useful operation of thefcircuit in some applicationsWhere the leakage currents would not be detrimental to the particularload. Diode 33, inthe load circuit, provides low resistance to the loadcurrent when polarized, as shown, by means of potential source 29.However, when the voltage of poteritial source 19, at the base oftransistor 11, is greater than the voltage of potential source 29, atthe collector thereof, diode 33 is reverse biased and prevents currentfrompotential source 19 from entering the load circuit. It can thereforebe seen that diode 33 prevents reverse current from entering the load,which is essential 'for the protection of many load devices, and alsoprovides protection for transistor 11. It has been found that, byemploying diodes 25 and 33 and potential sources 19 and 2/9, withpolaritie as described, the current in the load circuit may beselectively varied in an essentially linear manner. by adjustment of themagnitude of current through the control circuit, as by adjusting theposition of the tap of rheostat 21. FIG. 2 shows a line 34 passingthrough a plot of control current values and corresponding load currentvalues. In this, graph the plotted values of current flow representcurrent flow in the direction of arrow 1 (FIG. 1), which is thedirection opposite to the direction ofbase circuit current how of atransistor during its operation as a conventional amplifier, and theplotted values of load current represent current dlow in the directionof arrow 1 which is the direction opposite to the direction of collectorcircuit verse direction. Control circuit diode 25 provides lowresistance to the control current when polarized as shown. When theVoltage of potential source 19, at the base of transistor 11, is lessthan the voltage of potential source 23, at the collector thereof, diode25 is reverse biased and prevents current from potential source 29 fromflowing in the control branch and back through the load. From the graphshown in FIG. 2 it can also be seen that diode '25 limits the loadcurrent to its maximum value and within its linear region. This maximumcurrent is that current which will passthrough the transistor when .apotential, of described polarity and in excess of the potential barrierof the transistor and diode in the load circuit, is applied across theemitter and collector, and the base circuit is open. This also serves toprotect the load device since further decrease of the positive biasapplied to the base of transistor 11 results in no increase of the loadcurrent.

It can therefore be seen that the presence of diodes 25 and 33 allowsthe circuit to operate only within its linear region, prevents reversecurrent through the load and establishes a maximum forward load currentregardless of the potential applied to the base of the transistor 11.The FIG. 1 circuit can function either as a relay, by actuation ofswitch 23,.0r as a linear continuous current control device, by closingswitch 23 and varying the resistance of rheostat 21.

In FIG. 2 is a curve showing the relationship between control currentand load current for the linear region of thedevice shown in .FIG. 1when operating as a continuous current control device. From this curveit can be seen that the load current is directly proportional to thecontrol current from somewhat less than one microampere to approximatelynine microarnperes. As previously explained, diode 33 prevents the loadcurrent from decreasing past zero and inthe reverse direction and diode25 prevents the load current from increasing beyond a predeterminedvalue.

In FIG. 3 is shown a modified form of the control device shown'in FIG. 1wherein theload circuit includes an A.C. potential source rather than aDC potential source. The load circuit comprises a first series loopincluding A.C.generator 35, load 37, diode 33, and the emitter'andcollector of transistor 41, and a second series loop including A.C.generator 35, diode 43, the emitter and collector of transistor 45 andload 37. The control circuit includes two separate control loops whereinthe first loop includespotential source 47, rheostat 4a, switch 51,diode 53 and the emitter and base of transistor 41 and the second loopincludes potential source 55, rheostat 57, switch 59, diode 61 and theemitter and base of transistor 4-5.

The operation of this circuit is as follows. During the positive halfcycle of generator 35, as shown, diode 39 provides low currentresistance and diode 43 provides high current resistance. Therefore,current flows clockwise in the first series loop and there is nocurrentilow in the second series loop. During the negative halt cyclediode 43 is conducting and diode .39 is non-conducting and current flowclockwisein the secondseries loop and doesnot flow in the first seriesloop. Therefore, load 37 receives an A.C. signalthe magnitude of whichis dependent upon the potential applied to the bases of transistors 41and 45. Transistors 41 and 45, of the NPN type, arereverse biased as isthe PNP transistor of the device shown in FIG. 1. It should be notedthat when diodes 39 and 43 are conducting, respectively, the emittersand collectors of transistors 4-1 and 45 are respectively reversedbiased. The function of diodes 39 and 53 and 43 and 61, respectively,are the same as diodes 33 and 25 of the FIG. 1 device.

In FIG. 4 is shown a modification of the FIG. 3 device. The basicdifference between the two circuits being that only a single controlcircuit is utilized for the two A.C. load loops in the FIG. 4modification. The load circuit comprises a first series loop includingA.C. generator 63,

load 65, diodes 66 and 67 and the emitter and collector of transistor 68and a second series loop including A.C. generator 63, load 65, diodes 69and 70 and the emitter and collector of transistor '71. The controlcircuit includes potential source '72, switch 73, rheostat '74, the baseand emitter of transistor 68, diodes 67 and 7t) and the base and emitterof transistor '71. The control current is isolated from the load bymeans of diodes 66 and 69. During the positive half cycle of generator63, current flows through the first load loop and during the negativehalf cycle it flows through'the second loadloop resulting in an A.C.load output which isproportional to the control current.

The device shown in FIG. '5 is a modification of the FIG. 1 device.The-FIG. 5 device provides separate control andload circuits havingsequential cutolis wherein a first series load loop includes potentialsource 31, diode 82, the collector and emitter of transistor 83 and load84 and a second series load loop including potential source 85, diode36, the collector and emitter of transistor 83 and load 87. The controlcircuit comprises a first series loop including potential source 88, thebase and emitter of transistor 83, diode 89, rheostat 9t) and switch 91and a second series loop including potential source 88, the base andemitter of transistor 83, diode 89, rheostat 92 and switch 93. Theoperation of this control circuit is as follows: Assuming potentialsources 81 and 85 are of the same value and loads 84 and 87 are the samevalue, thenboth load loops will have the same operating ranges andcutotf points as previously described with relation to FIGS. 1 and 2. Inaddition, however, diodes 82 and 86 make it possible to use a singletransistor and different potentialsfor each of potential sources 31 and85 in order to obtain diiferent operating ranges for each of the loads.The provision of two control loops, one involving rheostat 90 and switch91, and the other involving rheostat 92 and switch 93, makesitpossibleto produce three distinct control points or operating conditions.Closing switch 91 provides one operating condition; closing switch 93provides a second operating condition; and closing both switches 91 and93, which places the resistances presented by rheostats 90 and 92 inparallel, provides a third operating condition. It is to beunderstoodthat'additional control and load loopscould be added in orderto provide a greater range of control.

Obviously many modifications and variations of the present invention arepossible in the light .of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A current control device including first and second transistors, anA.C. potential source and a load, a first load circuit including saidA.C. potential source, said load, the emitter and collector of saidfirst transistor and a first diode to prevent current flow through thefirst load circuit in the conventional direction of current flow throughsaid first transistorv between its emitter and collector connected inseries, a second load circuit including said A.C. potentialsource, saidload,the emitter and collector of said second transistor and a seconddiode to prevent current flow through said second load circuit in theconventional direction of current fiow through said second transistorbetween the emitter and collector connected in series, a first controlcircuit including current control means, a first DC. potential sourcepoled to generate a current flow through said first control circuit in adirec tion opposite to the conventional direction of current flowthrough said first transistor between its emitter and base, and the baseand emitter of said first transistor connected in series, a secondcontrol circuit including current control means, a second D.C. potentialsource poled to generate a current flow through said second controlcircuit in a direction opposite to the conventional direction of currentflow through said second transistor between the emitter and base, andthe base and emitter of said second transistor connected in series,whereby the output of said AC. potential source passes through saidfirst load circuit during one polarity of its cycle and through saidsecond load circuit during the other polarity.

2. The device of claim 1 including a third and fourth diode, seriesconnected in said first and second control circuit, to prevent currentflow through said control circuit in the conventional direction ofcurrent flow through the associated transistors between its emitter andbase.

3. In an electronic-relay circuit of the type employing a transistor andin which a control circuit through the base-emitter internal path of atransistor is adapted to be opened and closed to thereby selectivelyenergize or tie-energize a load circuit through the emitter-collectorinternal path of the transistor, said control circuit having a firstnon-coterminate section extending between the base of the transistor andthe emitter of the transistor, and said load circuit having a secondnon-coterminate section extending between the collector of thetransistor and the ernitter of the transistor, said emitter forming ajunction point common to the control and load circuits, theimprovements, in combination, comprising;

(a) said transistor being of the type having conventional unipolarcharacteristics in which predetermined conventional directions ofcurrent flow are defined for current flow through its base-emitter andemitter-collector internal paths, respectively,

(b) a first potential source having a first predetremined magnitude ofpotential serially connected in said first non-coterminate section ofthe control circuit and poled to cause a current to flow in a directionopposite to the conventional direction of flow through the base-emitterinternal path, a second potential source having a second predeterminedmagnitude of potential serially connected in said second non-coterminatesection of the load circuit and poled to cause a current to flow in adirection opposite to the conventional direction of flow through theemitter-collector internal path of the transistor, a first blockingdiode serially connected in said first non-coterminate section of thecontrol circuit and poled to present an open circuit to flow of currentin the conventional direction through the base-emitter internal path toisolate the first non-coterminate section of the control circuit fromcurrent bucking efiects as the result of load circuit current flow, anda second blocking diode serially connected in said second non-cotern Urninate section of the load circuit and pole to present an open circuitto fiow of current in the conventional direction through theemitter-collector internal path to isolate the second non-coterminatesection of the load circuit from current bucking effects as the resultof control circuit current flow, and (c) said first and secondpredetermined magnitudes of potential being chosen to cause thetransistor to operate in a mode of its operation characterized byoperation of the transistor to produce a current through the loadcircuit having a magnitude within a first range of values approximatelybetween zero and ten rnicroamperes and which magnitude variessubstantially linear inverse proportional relationship in response tocurrent through the control circuit having a second range of valuesapproximately between zero and two microamperes,

whereby the energizing of the load circuit by a current having apredetermined fixed magnitude, within said first range, may be reliablycontrolled by the opening and closing of the control circuit. 4. Acircuit in accordance with claim 3, and (d) selectively adjustablevariable resistance means serially connected in said firstnon-coterminate section of said control circuit for adjusting themagnitude of control circuit current to thereby permit pre-adjustment ofthe magnitude of load circuit current to a desired value within saidfirst range in accordance with said inverse relationship.

References Cited by the Examiner UNITED STATES PATENTS 2,728,857 12/55Sziklai 307-885 2,810,081 10/57 Elliot 30788.5 2,840,726 6/58 Hamilton307-885 2,928,036 3/60 Walker 321--46 X 2,953,738 9/60 Bright 321-472,962,603 11/60 Bright 307--88.5 2,988,688 6/61 Benton 323--22 FOREIGNPATENTS 1,064,608 9/59 Germany.

LLOYD MCCOLLUM, Primary Examiner.

ORIS L. RADER, MILTON O. HIRSHFIELD,

Examiners.

1. A CURRENT CONTROL DEVICE INCLUDING FIRST AND SECOND TRANSISTORS, ANA.C. POTENTIAL SOURCE AND A LOAD, A FIRST LOAD CIRCUIT INCLUDING SAIDA.C. POTENTIAL SOURCE, SAID LOAD, THE EMITTER AND COLLECTOR OF SAIDFIRST TRANSISTOR AND A FIRST DIODE TO PREVENT CURRENT FLOW THROUGH THEFIRST LOAD CIRCUIT IN THE CONVENTIONAL DIRECTION OF CURRENT FLOW THROUGHSAID FIRST TRANSISTOR BETWEEN ITS EMITTER AND COLLECTOR CONNECTED INSERIES, A SECOND LOAD CIRCUIT INCLUDING SAID A.C. POTENTIAL SOURCE, SAIDLOAD, THE EMITTER AND COLLECTOR OF SAID SECOND TRANSISTOR AND A SECONDDIODE TO PREVENT CURRENT FLOW THROUGH SAID SECOND LOAD CIRCUIT IN THECONVENTIONAL DIRECTION OF CURRENT FLOW THROUGH SAID SECOND TRANSISTORBETWEEN THE EMITTER AND COLLECTOR CONNECTED IN SERIES, A FIRST CONTROLCIRCUIT INCLUDING CURRENT CONTROL MEANS, A FIRST D.C. POTENTIAL SOURCEPOLED TO GENERATE A CURRENT FLOW THROUGH SAID FIRST CONTROL CIRCUIT IN ADIRECTION OPPOSITE TO THE CONVENTIONAL DIRECTION OF CURRENT FLOW THROUGHSAID FIRST TRANSISTOR BETWEEN ITS EMITTER AND BASE, AND THE BASE ANDEMITTER OF SAID FIRST TRANSISTOR CONNECTED IN SERIES, A SECOND CONTROLCIRCUIT INCLUDING CURRENT CONTROL MEANS, A SECOND D.C. POTENTIAL SOURCEPOLED TO GENERATE A CURRENT FLOW THROUGH SAID SECOND CONTROL CIRCUIT INA DIRECTION OPPOSITE TO THE CONVENTIONAL DIRECTION OF CURRENT FLOWTHROUGH SAID SECOND TRANSISTOR BETWEEN THE EMITTER AND BASE, AND THEBASE AND EMITTER OF SAID SECOND TRANSISTOR CONNECTED IN SERIES, WHEREBYTHE OUTPUT OF SAID A.C. POTENTIAL SOURCE PASSES THROUGH SAID FIRST LOADCIRCUIT DURING ONE POLARITY OF ITS CYCLE AND THROUGH SAID SECOND LOADCIRCUIT DURING THE OTHER POLARITY.